From acute defense to prolonged metabolic homeostasis: Insights into microalgae responses to PVC microplastic...

Microplastics (MPs) persist in environment, exerting long-term stress on aquatic ecosystems. As pivotal primary producers, microalgae are highly sensitive to environmental stress, with their growth and physiology impaired by MPs. Most existing MP toxicology studies are limited to short-term exposure (< 5 days) and macroscopic microalgal physiological indicators. Here, typical aquatic microalgae Scenedesmus obliquus (Chlorophyta) and Synechococcus sp. (Cyanophyta) were selected as test organisms to explore their response and regulatory mechanisms under acute and prolonged polyvinyl chloride (PVC) MP exposure by monitoring dynamic intracellular dissolved organic matter (IDOM) and metabolism over a 12-day culture. Acute exposure (days 0-4) induced species to resist stress via membrane lipid repair (S. obliquus) and enhanced signal transduction (Synechococcus sp.). Prolonged exposure (after day 4) presented reduced resistant levels, with these two algae exhibiting specific metabolic regulation-membrane lipid stabilization and optimized resource allocation, respectively. Divergent metabolic responses reflected species-specific differences driven by distinct cellular structures. Moreover, the transition from humic-dominant IDOM in the acute phase to protein-dominant IDOM during sustain exposure period reflected a strategic shift from rapid regulation to metabolic homeostasis, highlighting the potential of protein-like/humic-like ratio as a diagnostic proxy for algal physiological status under PVC-MP stress. This study better illustrates microalgal metabolic regulatory mechanisms on acute stress to prolonged bio-regulation under PVC-MP stress, providing clear evidence for evaluating the potential ecological impacts of MPs.